Brush and brush holder assembly



June 30, 1970 $550K ET AL BRUSH AND BRUSH HOLDER ASSEMBLY Filed Aug. 15,1966 INVENTORS ALBERT L. SEBOK, JOHN H.

3,518,475 BRUSH AND BRUSH HOLDER ASSEMBLY Albert L. Sebok, Tallmadge,and John H. Porter and Everal B. McBroom, Jr., Kent, Ohio, asslgnors toAmetek, Inc., a corporation of Delaware Filed Aug. 15, 1966, Ser. No.572,565 Int. Cl. H01r 39/40 US. Cl. 310-245 8 Claims ABSTRACT OF THEDISCLOSURE A saddle type constant force feed spring, with end coilsseated on outer ends of, and its reaches in longitudinal recesses of,opposed walls of a rectangular guide passage of a brush tube, has a yokeportion transversely seated in a wedge thrusting on V-notch-definingends of split brush elements. The Wedge, sideand end-guided by thepassage and end-notched to accommodate connecting respective pig-tails,spaces the reaches from the half-elements so that without interferencethe inner element ends are slidingly spread against the passage tominimize tilting and simultaneous bounce during operation, there byincreasing brush life.

The present invention relates generally to a brush and brush holderassembly for making a sliding type electrical contact with rotatingcommutators or slip rings in dynamo electric machines; and moreparticularly relates to improvements in a so-called longitudinally splitbrush and brush holder assembly therefor.

'For convenience the invention will be discussed in termsof brush holderassemblies for commutator-type electric motors; but it is to beunderstood that the invention has wider application, as will be apparentto one skilled in the art.

'In both prior practice and the patented art, brush holder assembliesfor electric motors, having an elongated, usually carbonaceous, brushlongitudinally advanced or fed against a commutator or similar movingpart, have appeared with the brush longitudinally split rather thansolid, in other words, having the brush comprised of two similarelements, each having half of the thickness of the correspondingconventional solid brush which oculd be used in the holder. In suchcases, by suitable spring or pressure means, the brush holder assemblyfed the two elements more or less in longitudinal contact and generallyas a conventional unitary brush would be fed; the plane of the split orof abutting longitudinal faces passing through or at least extendingparallel to the axis of the commutator. An advantage of suchlongitudinally split brush was expected to be a diminution of themutually aggravating events of heavy arcing and pitting of thecommutator, therefore increase of brush life which is adversely affectedby heavy pitting. This advantage was anticipated on the theory that anybrush bouncing or chattering, caused by transit of successive commutatorsegments, especially uneven segments or rough segments, would result inless arcing with the current fed through the two brush halves because ofa greater probability of conductive contact with the commutator throughat least one brush half than would be the case with a solid brush.

It has further been proposed in the prior art both with unitary andsplit type brushes, to minimize as far as possible the continuousdecrease, with brush wear, of brush contact pressure which has beencharacteristic of the con- United States Patent ventional brush feedssuch as compressed helical brush feed springs, to use constant forcebrush feed spring including use of saddle type constant force spring,having a yoke portion engaging endwise a split brush distal from thecommutator and parallel side reaches extending along opposite sides ofthe brush within the brush holder guide tube. In such prior art, it hasbeen further proposed that the distal ends of the split brush halves beeach tapered to form therebetween a V-notch or recess receiving a wedgeelement with the yoke portion of a saddle type spring bearing upon thewedge. By this means it was thought that one cause of brush chatterwould be eliminated, namely the swing of one or the other of the brushelement outer ends about pivot points at the bottom region of the brushguide tube or of one element relative to the other, a consequence of thenecessary clearance and manufacturing tolerances between the combinedthickness of the brush elements and the internal dimensions of the brushguide tube wall portions embracing the same.

It is with this type of brush structure that the present invention ispatricularly concerned by providing an improved relatively simple andlow-cost brush and brush holder assembly of the character describedwherein not only are chatter and bounce minimized and certain dragelfects by the spring avoided, but also wherein provision is made forensuring little possibility of any notable conduction of current by theconstant force spring thereby eliminating limitations of priorstructures, especially respecting the heating elfect of currentconducted by such spring, detrimental to the spring characteristics andthe constancy of its applied feeding force.

It is then the general object of the present invention to provide animproved longitudinally split brush and holder assembly therefor.Another object is provision of a relatively simple brush holder andbrush assembly affording increased brush life. It is another object toprovide in an assembly of split brush and holder therefor of improvedmeans for feeding current to the brush elements. It is a still furtherobject to provide in a device or assembly of the character described ofan improved means for applying the force of the constant force typespring to the split brush portions. Another object is to provide meansfor retaining a worn brush stub and spring of the type described in theholder.

Other objects and advantages will appear from the following descriptionand the drawings wherein:

FIG. 1 is a generally longitudinal, though somewhat irregular, sectionthrough a brush holder assembly taken substantially as indicated by thelines -1-'1 in FIG. 2 or FIG. 3;

, FIG. 2 is another longitudinal section of the assembly takenapproximately as indicated by the lines 2-2 in FIG. 1 and FIG. 3;

FIG. 3 is an enlarged view of the assembly, tions being broken away,taken distal from the commutator;

FIG. 4 is an enlarged perspective view of a brush end spreader or wedgeelement;

FIG. 5 is a detail of the brush feed spring; and

FIG. 6 is an enlarged schematic representation indicating approximately,in exaggerated form, the geometry and mode of action of certain featuresor structures of the assembly.

In the embodiment of the invention shown in the draw ings, a brushholder assembly for making conductive contact with the rotating elementsuch as a commutator,

certain porat the end of the assembly suggested by a dashed outlineportion C, comprises as principal elements a conductive metal holder orguide tube T, received and secured in an insulating tube I engaged bysuitable known means (not shown) securing the entire assembly to butinsulated from the environment such as a motor end bracket; brush meansB comprised of two identical half portions representing, as it were, alongitudinally split brush, slideably guided for longitudinal feedmovement in and connected to the tube T; a saddle type constant forcebrush feeding spring S (see also FIG. with is transverse yoke portion 11bearing on the outer end region of the brush means B through themediation of a spreader or wedge element W (see also FIG. 4) and havingextended side portions 12, each reaching downwardly respectively from awedge edge, in a longitudinal recess of the brush tube and in spacedrelation between the adjacent brush and brush tube wall, to terminate inthe residual coiled portion 13 engaging the bottom end of the brushtube. As the brush wears and is fed inwardly the side portions feedthemselves into the bottom coiled portions 13 by the characteristicaction of this type of spring.

The brush may be formed of any of the conventionally used material, suchas carbon; and the spring may be a NEGATOR saddle type, for example.Also for the brush lead connection to the holder (not shown) variousknown and obvious expedients may be used.

The general form, particularly the cross section of the brush tube T, isseen, especially from FIG. 3, to be of a conventional form currentlyused for unitary or solid brushes of rectangular cross sectionlongitudinally fed against the commutator by an end-bearing helicalcompression spring; being formed either as an extrusion of the sectionindicated or formed from sheet metal, usually brass, with a longitudinaldove-tail type interlock seam along one of the arcuate side portions.The tube section is basically a rectangle with opposite sidesdimensioned to correspond to the total brush cross section withappropriate clearances and with longer sides respectively bowedoutwardly into portions of concentric circular arcs, the diameter acrosswhich in a conventional brush tube being slightly larger than theintended helical brush feed spring diameter.

Here such a tube, readily available from commercial sources, affords notonly paired parallel straight longitudinal surfaces requisite for brushguiding, but also the arcuate portions serving as the previouslymentioned longitudinal recesses for accommodation of the side reaches 12of the brush spring.

Spaced downward from the upper brush tube end in the opposite flatparallel side walls 16, barbs 17 are outwardly staked or sheared, withupper ends free as shown in FIG. 2, whereby the tube T may be insertedfrom an open upper or outer end of the insulation tube I until suchbarbs come into coincidence and retaining engagement with correspondinginsulation tube inside wall recesses or apertures 18 affording shouldersengaged with the top walls of such recesses especially effective toimmobilize the guide tube T in the insulation tube I against anytendency to move radially away from the commutator.

A tab 19 is sheared and bent outwardly at right angles from the outerend of one tube wall 16 for a soldered or spot welded attachment of thefree ends of the respective flexible conductor brush pigtails 21, 22,each received and secured by conventional means in an aperture in avertical face resulting from cutting out of the upper end corner of thebrush at 20 to form a recess which with a coincident cut-out thereabovein the spreader wedge W and the region between the top of wedge W,spring yoke 11 and the surrounding top end region of tube T affords anaccommodating space for the slack length of brush pigtails in a newlyinstalled holder assembly. The pigtail length preferably is selected soas to stop brush feed at a point before the brush has worn into thepigtail connecting region or cut-out 20, thereby to retain the brushstub and spring safely in the holder.

At the bottom of the tube T, centrally located on the end edges of bowedwall portions 15 are shallow notches 29 of width corresponding to thespring stock width, through which respectively pass the outermost turnsof the residual portion of the coiled ends 13, lying outside the tube,leading into the straightened reaches 12 which both permit a closersetting of the holder to the commutator (on the order of inch spacing)and also engage edgewise the lower ends of each reach near the coil 13to locate the spring.

The form of the spreader or wedge element W and of the unstressed normalor uninstalled form of a NEG- ATOR saddle type spring S are seenrespectively in FIG. 4 and FIG. 5.

The brush spreader or wedge device W has wedging faces forming adihedral angle of and bearing on respective 45 tapered or angular endfaces at the upper ends of the brush elements; and has a central springyoke seat formed across the top. The wedge length corresponds withslight free sliding clearance to the internal length of the tubecross-section, but its top width is slightly greater than the tuberecangular width; andv the wedge at each side has end notches permittingwedge end portions 26 to project into and be guided by right anglelongitudinal surfaces of the tube while wedge top longitudinal edgeportions project slightly into the arcuate recesses 15 of the guide tubeT to support the spring yoke in such manner that the side spring reachesare in the tube longitudinal recesses spaced from the brush elementsides and tube sides. Over the location of each brush element cut-out20, the wedge end notching is correspondingly enlarged for brush pigtailaccommodation. The element W thus is rotationally sypmmetrical withtwo-fold symmetry about an axis perpendicular to the dihedral edge andlying in a bisecting plane of the angle.

, The wedge W is thus oriented by the tabs 26 slideably guided andsupported endwise by tube walls 16, and to some degree sideways by theouter corners of the tube rectangle.

The wedge or spreader element W may be considered as fabricated from aright angle metal section (e.g., hard brass) providing sides or plates25 equal in dimension from the wedge dihedral edge or apex to the freelongitudinal edges, and length corresponding (with the tube clearance)to the brush width or longer internal cross-section length dimension ofthe tube, the span between the opposed free edges of the plate beingsomewhat greater than the inside rectangular width. At each end aportion is cut off entirely across a respective plate 25 at a locationwhich will fall over a brush recess 20 and partially up the end of theother plate to afiord the described brush pigtail accommodating notches,and also forming tabs or lugs 26 as the aforementioned guided wedge endportions, each further narrowed or defined by corner notching each plateinward from the free edge, whereby the free edge portion is reduced inlength sufficiently to project into the longitudinal recesses formed bythe bowed wall portions 15.

A flat 27 of length corresponding to the spring stock width is milledalong each plate edge, centrally of the wedge length, such flatscoplanar and forming in the edges opposed aligned notches as the springyoke seat upon or within which is received and located the straighttransverse yoke portion 11 of the spring S. These flats preferably aremilled down into coincidence with the outermost or remote parallel edgesof the longitudinal end faces, such longitudinal edges having a spacingcorresponding to the internal length of yoke 11.

The wedge W keeps the lateral portions of the spring, especially justbeneath the yoke, from collapsing or pinching inward on the brush pairas well as serving in conjunction with tube bottom notches 29 to trap orlocate the spring edgewise.

In FIGS. 1 and 3 no attempt is made to show the brush wedging orspreading effect of the element W on the brushes, this effect beingpresented rather schematically and in exaggerated manner by FIG. 6. ThisFIG. 6

shows also a structural refinement at the very upper end of each brushelement, comprising the termination of the brush actually in a narrowflat end face 31 and a slight external taper or fiat face 32 at 30 tothe external face, having respective widths on the order of 0.035 inchfor a /8 by by 1% inch brush half element, giving a broken corner whichwill not wedge between the adjacent spreader side plate 25 and springreach 12, giving free action in brush feed.

Assuming clockwise commutator rotation in FIG. 6, the lower ends of thebrush elements are dragged by the commutator to the right; at the guidetube bottom edge region, the right half bearing against the shortresidual straight portions 15a of the tube rectangle and the left halfbearing against the right half, so that practically the total of allcorresponding tube and brush tolerances and clearances appears as thebottom spacing between the left side of the left half element and thebottom edge of residual straight portions 15a of the left tube wall. Theupper ends of the halves, however, are spread by the wedge W intoengagement with such tube Wall portions 15a, and thus effectivelyprevented by the wedge face and wall contacts from swinging or pivotingabout the bearing lines of contact near the bottoms of their respectiveright faces. The upper longitudinal edges of the wedge in keeping thespring reaches spaced out in the recesses formed by side bows 15 thusensure that the brush upper ends bear against the tube and not againstthe yieldable spring reaches.

As an example of brush life prolongation, may be noted the fact that ina test of a brush holder and split brush assembly as above described ina continuously operating motor, after five thousand hours the motor wasstill operating with good commutation, with the commutator in goodcondition, and with a brush length yet remaining which would indicatesome thousands of hours of further brush life to be expected; incomparison with a maximum expected brush life of about 1000 hours in thesame motor for a comparably sized brush holder with solid brush andhelical feed spring.

Though for convenience of description the ends of the assembly remotefrom and proximate to the commutator may be referred to.as upper ends ortop and lower end or bottom, or similar terms of orientation may be usedfor 1 the assembly or parts thereof corresponding to the drawingorientation, there is, of course, no implication that use of theassembly is restricted tosuch orientation. Moreover, it is to be notedthat though the location of elements is generally shown as for anassembly with new brush in operative position with the spreader W spaceddownward from the top end of the holder, the brush pigtails for clarityare not shown laid down in the defined space adapted to receive thesame, even with an end cap applied thereover, if desired. Also where thelongitudinal brush guide passage; provided by the rectangularly disposedinside wall portions of tube T, is referred to as having a cross-sectioncorresponding to or conforming to the external cross-sectional shape ofthe split brush, this is to be understood as contemplating normalmanufacturing tolerances for the necessary free sliding clearances.

What is claimed is:

,1. A brush and brush holder assembly for dynamoelectric machines or thelike wherein a longitudinally centrally split brush is used and heldwith the plane of the split extending substantially transverse to thedirection of movement relative to a surface with which the brush is toafford conductive moving contact, comprising:

a brush guide tube providing a longitudinal brush guide passage,

a pair of like brush half elements slideable longitudinally in the guidetube for simultaneous feed toward said surface in longitudinally facingrelation as a split brush,

the upper ends of said brush halves having opposing longitudinal facesthereof terminating in inclined faces forming a V-notch at the splitbrush top, the cross-section of said guide passage conforming generallyto the external cross-sectional shape of and split brush, a brushspreading wedge in said V-notch having upper longitudinal edge portionslocated above and projecting outboard of the upper ends of therespective brush halves, whereby the said upper ends are spread awayfrom each other into contact with opposite sides of the tube passagewhen the split brush bears on a said surface, a saddle type constantforce brush feed spring having a yoke portion seated on the top of andextending transversely across said upper longitudinal edge portions ofthe wedge at right angles to the longitudinal split of the split brush,and respective side reaches extending from the ends of the yokedownwardly within the guide tube and terminating in end coils, whereintothe side reaches tend to self-wind and exert brush feeding tensionthrough the reaches on the yoke, said end coils secured at the bottomregion of the tube,

said tube having longitudinal recesses in opposite wall portions of saidpassage receiving with clearance the respective, outboard projecting,edge portions of said wedge and for accommodating said spring sidereaches in spaced relation from the guide tube and the respective brushhalves.

2. The assembly of claim 1, wherein each brush half has a top end cornercut-out wherein a respective pigtail end is secured, the cut-outs in thesplit brush occurring under opposite ends of said wedge, said wedgehaving correspondingly located end cut-outs above the brush cutouts, andsaid wedge spaced inwardly from the proximal end of the guide tube whenthe unworn split brush is in operating position, whereby a pigtailaccommodating space is defined in said passage between the said end ofthe tube, the tube walls and the wedge.

23. The assembly of claim 2 wherein the cut-outs of said wedge leavewedge end portions guideable by opposed wall portions of the tube.

4. The assembly of claim 2 wherein said guide tube is a conductive tube,said guide tube having an anchor formation adjacent; said defined spacefor attachment of the other ends of the pigtails; and including aninsulation tube surrounding the greater part of said guide tube where bythe assembly may be clamped in insulated relation in the environment ofuse.

5. The assembly of claim 1 having a respective pigtail connected to theupper end of each brush half and to an anchor point at the upper endregion of said assembly with the pigtail of such length that it stopsbrush feed advance by said spring at a preselected extent of brush wear,thereby to retain the brush halves, wedge and spring in said guide tube.

6. The assembly of claim 1, wherein said wedge has a central transversespring yoke seat formed across its top and the guide tube has onopposite sides of its bottom end region seat formations for therespective coil-terminated end portions of the spring.

7. The assembly of claim 6 wherein said wedge has end portions guided byopposed wall portions of said tube.

8. The assembly of claim 1, wherein said wedge has end cut-outs locatedon opposite sides of the wedge apex, said brushhalves havingcorrespondingly located respective end corner cut-outs beneath the wedgecut-outs wherein a respective pigtail end is secured, and said wedgeReferences Cited UNITED STATES PATENTS Harris 310-247 Gordon 310-247Sievert 310245 Welch 310247 Sekyra 310247 FOREIGN PATENTS Great Britain.France. Germany. Germany. Germany. Germany.

MILTON -O. H'IRSHFIELD, Primary Examiner 10 M. O. BUDD, AssistantExaminer US. Cl. X.R.

